This application claims the priority of German Patent Application, Ser. No. 101 12 532.1, filed Mar. 15, 2001, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to an air-cooled electric machine, and more particularly to an air-cooled electric rotary machine of a type having a stator with a laminated stator core having axial ends terminating in winding end portions, and a rotor spaced from the stator at formation of an air gap therebetween.
German Pat. No. 672,623 describes a cooling arrangement for closed electric machines, in particular three-phase motors. Disposed inside the closed machine are two fans for generating a flow of cooling air which is re-cooled by closed channels, or groups of channels, disposed on the outer surface area of the machine and circulated by a stream of coolant to define an outer coolant flow. At the axial ends, an inner coolant flow is routed by deflection walls through a looped path from one longitudinal channel or channel group in opposite direction to the following longitudinal channel or channel group.
This cooling arrangement suffers shortcomings because it requires the provision of two fans, one for each axial end of the stator core, in order to implement the looped deflection of the air stream. The use of two fans heightens the probability of a breakdown of the cooling action, and higher production costs are incurred compared to a system that would employ only one fan. Moreover, the presence of two separate cooling systems is also disadvantageous because heat has to be transferred from the inner cooling system to the outer cooling system. In accordance with the given thermal transmission coefficient, the cooling action is decreased by the cooling on the machine. The overall construction of the closed electric machine does not allow modular and variable constructions and thus is difficult to manufacture in various designs. This is true especially for types of machines that have different lengths, because separate constructions of cooling arrangements are required for each type, i.e. the construction of the machine requires a particular configuration of the cooling arrangement.
It would therefore be desirable and advantageous to provide an improved air-cooled electric rotary machine which obviates prior art shortcomings and which is so configured as to be applicable for different types of machines, in particular as far a machine length is concerned, while yet establishing a reliable and effective cooling action in a cost-efficient manner.
According to one aspect of the present invention, an air-cooled electric rotary machine, includes a stator including a stator having a stator core formed of laminations and having axial ends terminating in winding end portions, a rotor spaced from the stator at formation of an air gap therebetween, plural air channels, separated from one another and extending within and/or on the stator core, for allowing an air stream in complementary flow directions, a looped air stream conduction established by a directional deflection of the air stream at the winding end portions, and a single fan for cooling the stator by forcing the air stream to flow through the cooling channels and the looped air stream conduction.
The present invention resolves prior art problems by so structuring the electric rotary machine that only a single fan can be used for conduction of a sufficient air stream for cooling at least the laminated stator core. The air stream is conducted in separate cooling channels which can be formed in and/or on the stator core. Cooling channels provided in the stator core can be suitably formed, for example, by individually stamping the individual metal sheets of the stator core. The looped deflection of the air stream at the axial ends of the stator core allows an air stream in complementary flow directions. The looped air conduction is characterized by two factors. On the one hand, the air stream is guided about the winding end portions at the axial ends of the stator core, thereby following a circular, almost closed path and as a result assuming a looped configuration, and on the other hand the looped conduction of the air stream is established by separate cooling channels because of the necessity to reverse the flow direction by 180xc2x0.
When the stator core is cooled by only one air stream in only one direction, the temperature difference between air temperature and temperature of the stator core decreases as the air stream travels in the cooling channel. This cooling effect, which differs substantially and is dependent on the entry point of the cooling air, is counteracted when feeding air through separate cooling channels of the stator core. A temperature equalization is realized between the separate cooling channels in the stator at any location with respect to the longitudinal axis. When, for example, referring to the location on the stator core, which is characterized by the initial air entry into a cooling channel of the stator core, on the one hand, but also in a neighboring, separate cooling channel by the exit of the cooling air stream, on the other hand, a temperature equalization is realized there. The equalization is provided at this locationxe2x80x94in this areaxe2x80x94by air which has cooled a winding end portion, on the one hand, and has flowed already through two winding end portions and in addition has passed twice cooling channels in the stator core. As a consequence, a mean cooling action is established for each axial area of the stator core.
The fan for generating the air stream may be configured as an internal machine-own fan. This is advantageous in conjunction with complete systems. The machine-own fan may be positioned on one side of the axial ends of the stator core behind the end winding portions and constitutes the starting point for the air stream being forced through the machine. In the description, the term xe2x80x9cmachine-own fanxe2x80x9d will denote merely the fact that the fan is part of or incorporated in the electric rotary machine. Hereby, it is, of course, conceivable to position the fan also on different locations of the machine. The air streams should then be so conducted as to establish a flow in a manner according to the invention.
In particular, when larger air-cooled electric rotary machines are involved or even groups of electric rotary machines, the air cooling of the electric rotary machine may also be implemented by an external fan, i.e. a fan that is positioned outside the electric rotary machine. The air stream produced by the external fan has at least one entry into the coolant system of the electric rotary machine. The utilization of an external fan has the advantage to allow the application of a single fan for different electric rotary machines or for different units to be cooled. An external fan, which is not part of the electric rotary machine, can also be more easily replaced. Two types of external fans can be referred to here by way of example. When the fan should not be positioned on the shaft of the electric rotary machine, it is possible to place the fan on the housing of the electric rotary machine. When ventilating several electric rotary machines with one fan, air channels are provided which distribute and feed the air to the individual electric rotary machines.
Regardless whether an internal fan or an external fan is involved, at least one exit zone is provided for the air stream. The looped conduction of the air stream at the end faces of the stator core is established by measures that effect a routing of at least a portion of the air stream radially through the winding end portions. Examples of such measures includes the provision of cap-like formed parts, air guides or air baffles, which may interact separately or in concert with a motor housing. Depending on the configuration of the winding end portions, the radial air conduction on the end faces of the stator core may be implemented by different configurations. Cast winding end portions are cooled by the cooling air stream along the outer surfaces of the cast product. When cooling channels are provided inside the cast product, a cooling action is implemented directly inside the winding end portions and heat is carried away. When the winding end portions are not cast products, at least parts of the cooling air stream can be conducted through the winding end portions so as to realize not only a heat dissipation via the outer surface of the winding end portions but also by the air stream routed through the winding end portions.
The air stream, or air streams, inside the machine can suitably be used so as to assist also in cooling a bearing unit provided for supporting the shaft of the electric rotary machine. Hereby, a bearing has cooling surfaces which project into the area of the cooling air stream. Through the assistance of air guides, the air stream or diversions of at least portions of the air stream can be routed to the bearings. The bearing or bearing end plate may have surface-enlarging structures for better cooling effect. In this way, bearings can be cooled by the air stream present in the machine.
As an alternative to the integration of cooling channels in the stator, the cooling effect may also be implemented in accordance with another embodiment of the present invention, through arrangement of a cooling jacket which has formed therein the cooling channels. There are many ways to integrate the cooling channels in the cooling jacket. Examples include casting or material-removing processes. The stator is surrounded at least partially by the cooling jacket, whereby the cooling channels are provided separate from one another for flow of air. The cooling jacket may be made of a same material as the formed parts at the axial ends of the stator core. The use of a cooling jacket is advantageous because there is no need or only a slight need for modifications of already existing stator concepts or stator designs, as the cooling jacket can already be best suited to the stator core at hand, in particular to the stator length. A standard machine, e.g. standard motor, can thus be retrofitted with the cooling system according to the present invention through execution of only few modifications.
According to another feature of the present invention, each axial end of the stator core has attached thereon at least one cap-like formed part for routing the air streams through the complementary air channels alternately and separately from one another in opposite radial directions. The air streams flowing in opposite radial directions are suitably routed within the caps through the winding end portions. It is therefore possible to conduct the air stream along the outside of one formed part in a direction radially away from the shaft whereas the air stream on the inside of the formed part, which at least partly surrounds the winding end portions, flows in the direction of the shaft center. As a consequence of the opposite axial directions, the looped conduction of the air streams is realized whereby the air streams are guided through or over the stator, and then deflected to flow along the end faces of the stator core in the 180xc2x0 opposite direction.
When placed on both axial ends of the stator core, the cap-like formed parts are suitably identical. An identical design of the cap-like formed parts saves costs, when manufacturing the cap-like formed parts and the air-cooled electric rotary machine.
For economic and manufacturing reasons, it is advantageous to minimize the number of components for the electric rotary machine. Therefore, it may be desired to manufacture the cap-like formed part as well as the cooling jacket of single-piece configuration. Suitably, the cooling jacket and at least one cap-like formed part are configured of single-piece construction in which the stator and the rotor can then be simply inserted. In this way, the cooling jacket provides a closed, cylindrical part in which a major portion of the heat-generating sources of the air-cooled electric rotary machine are located.
Surface-enlarging elements may be placed in the cooling channels of the stator core for improving the heat transfer to the coolant. Thus, in air-cooled electric rotary machines with cooling channels, two different machine types can be realized with different cooling action. The surface-enlarging elements are made of heat-conducting material to improve the cooling effect of the system, when originally integrated or even subsequently added.